This invention relates to a power assisted vehicle and more particularly to a power assisted that is capable of operating in significantly different modes.
There have been proposed a wide variety of types of manually powered vehicles. A number of these vehicles also offer the option of power assist. In some vehicles the power assist is of a type where the prime mover provides the substantial motive force for the vehicle under at least certain operator selected conditions. Another type of power assisted vehicle, and one which has great popularity, is one wherein the amount of power assist is tailored to the operator's manual input force. As a result of this, the power assist generally does not provide the sole mode of power for the vehicle. Rather, the vehicle maintains its manually operated feel but the load on the operator is reduced because the power assist is proportional to the operator input force.
With this latter type of vehicle, there may still be some times when the power assist in combination with the manual force input is not sufficient to propel the vehicle. For example, in bicycles or other land vehicles, they may be some hills that are so steep that the rider cannot, even with power assist, pedal up them. In these instances, or under other circumstances, the rider may wish to walk alongside of the vehicle or behind it and push it. However, under these circumstances, the power assist mechanism can actually make pushing of the vehicle more difficult than if no power assist would be provided.
There have been proposed ways wherein the pushing of the vehicle will in essence disable the power assist mechanism so that the operator need not drive the prime mover of the power assist mechanism when he is pushing the vehicle. There have also been proposed systems wherein the operator may switch on the power assist when pushing so as to augment his manual force to assist in pushing of the vehicle. Such an arrangement is shown in my U.S. Pat. No. 5,226,501 issued Jul. 13, 1993, entitled Electric-Motored Bicycle, assigned to the assignee hereof.
Although this type of arrangement has a number of advantages, the characteristics of the motor chosen for the power assist is such that it is not particularly efficient under low speeds and when high torque is required. The basic motor is designed so as to operate at higher speeds and hence is not efficient and does not generate large amounts of torque under this low speed pushing condition. Thus, the assist is not as great as desired and furthermore operation in this mode can deplete the power of the battery.
It is, therefore, a principal object of this invention to provide an improved propulsion system for a primarily manually-powered vehicle wherein the characteristics of the power assist can be changed manually or automatically to suit specific running conditions.
It is a further object of this invention to provide an improved electric motor assist for a manually operated vehicle wherein the electric motor is capable of operating in different modes in response to different conditions.
It is a still further object of this invention to provide an electric motor power assisted vehicle wherein the electric motor is capable of operating in at least two different modes which can be selected either manually or automatically to provide optimum running under all conditions and also insure long battery life.